Cooling apparatus is conventionally associated with the internal combustion engines by which most motor vehicles are propelled. When weather conditions necessitate heating of the cabin of the vehicle, the heat which is removed from the engine by the cooling apparatus is sufficient to provide this heating of the cabin once the engine has reached its normal operating temperature. By contrast, if the vehicle is propelled by an engine or motor which does not generate much heat --and in particular, an electric motor--the heat which is recovered by cooling this motor is not always enough to ensure satisfactory heating of the cabin. Accordingly, under these circumstances an auxiliary heat source has to be provided, for example an electric radiator, in order to ensure that sufficient heat is available.